Nice looking work there. Clean.

Through the little detective work I've been able to do, I developed a couple ideas. Could be right or wrong.

1. The Street Dominator appears to be the benchmark manifold for the M1 single planes, MP even sold it for quite awhile and advertised it as the best thing since the invention of the zipper. The benchmark had the universal carb pad, and maybe MP assumed that was an important feature that most customers wanted?

2. Super Stock, for a '72-up application, maybe? Although the intake can be cut as needed, maybe Shep wanted to make life somewhat easier?

But that idea doesn't hold water for the dual plane intakes, so feel free to print this, tack it to the wall and throw darts at it. The dual planes should also had the universal flange, IMO.